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Case of the Week #270

Clinical History:

A 65 year old man presented with multiple intestinal and mesenteric nodules. A nodule was excised and submitted in multiple pieces.

Micro images:

What is your diagnosis?

Diagnosis:

Epthelioid Gastrointestinal Stromal Tumor, Plasmacytoid variant

Discussion:

These immunostains were performed:

Left to right: CD34, CD117, CD38

Left to right: AE1-AE3, S100, vimentin

Gastrointestinal stromal tumors (GISTs) differentiate along lines of the interstitial cell of Cajal, the gutís pacemaker cell. Behavior varies by site. In the small bowel, 30-50% of tumors have malignant behavior. The median patient age for small bowel GIST is 67 years, and patients often present with large, bulky masses that may be well circumscribed. Most (70%) tumors have the classic spindle cell pattern, but 20% are epithelioid and 10% are mixed. Epithelioid tumor cells are usually malignant appearing, with abundant eosinophilic cytoplasm.